Tonian

Tonian
1000 – ~720 Ma Pha. Proterozoic Archean Had.
A map of Earth as it appeared during the late Tonian, c. 750 Ma
Chronology
−1000 — – −980 — – −960 — – −940 — – −920 — – −900 — – −880 — – −860 — – −840 — – −820 — – −800 — – −780 — – −760 — – −740 — – −720 — – M ♇ N e o p r o t e r o z o i c Stenian Tonian Cryogenian       ← First sponge-like animal?[1] ← Beginning of Sturtian glaciation ← Sharp drop in Stromatolite Population[2] ← End of Boring Billion
Etymology
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Period
Stratigraphic unit	System
Time span formality	Formal
Lower boundary definition	Defined chronometrically
Lower GSSA ratified	1991[3]
Upper boundary definition	Redefined chronometrically with an interim calibrated age of c. 720 Ma. GSSP is in progress.[4] (Previously defined chronometrically as 850 Ma)[3]
Upper boundary definition candidates	The first appearance of widespread glaciation.[5]
Upper boundary GSSP candidate section(s)	To be determined

The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic Era and followed by the Cryogenian.

Rifting leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya.